Exciton Phenomena in Functional Materials from Many-Body Perturbation Theory

Theoretical predictions of excited-state phenomena in complex materials can lead to better understanding of nanoscale energy conversion mechanisms, for instance in emerging photovoltaic and photocatalytic systems. In such applications, correlated electron-hole excitations, called excitons, often serve as carriers in the energy transfer processes. Structural complexities, such as reduced dimensionalities, interface compositions, and the presence of impurities, are closely coupled to exciton properties and decay processes. In this talk, I will describe a computational approach to study the excitonic phenomena in materials of structural complexity, using many-body perturbation theory within the GW and Bethe-Salpeter equation (GW-BSE) approach. I will discuss the effect of heterostructures and point defects on optical and excitonic properties in layered transition metal dichalcogenides, where a mixed nature of the electron-hole interactions lead to unique optical signatures and structurally-tunable selection rules. I will further present a new approach to study exciton decay processes from first principles, based on GW-BSE. I will demonstrate this approach for the case of multiexciton generation processes in organic crystals, and show a newly discovered exciton-exciton interaction mechanism related to crystal packing and symmetry.